Syncthing is an open-source file synchronization client/server application,
written in Go, implementing its own, equally free Block Exchange Protocol.
All transit communications between syncthing nodes are encrypted, and all nodes are uniquely identified with cryptographic certificates.

Starting Syncthing

Run Syncthing

Note: You can run multiple copies of syncthing, but only one instance per user as syncthing locks the database to it. Check logs for errors related to locked database.

System service

Running Syncthing as a system service ensures that it is running at startup even if the user has no active session, it is intended to be used on a server.

Enable and start the syncthing@myuser.service where myuser is the actual name of your user.

User service

Running Syncthing as a user service ensures that Syncthing only starts after the user has logged into the system (e.g., via the graphical login screen, or ssh). Thus, the user service is intended to be used on a (multiuser) desktop computer. To use the user service, start/enable the user unit syncthing.service (i.e. with the --user flag).

Syncthing-GTK

Syncthing can also be launched by syncthing-gtk. Use interface UI settings to start syncthing-gtk at startup, and to state whether to launch the syncthing daemon.

When launching the syncthing daemon using both systemd and syncthing-gtk, it might happen that two syncthing instances run concurrently leading to high CPU consumption: one launched by syncthing-gtk, and the other (slightly later) by systemd. To solve this, either avoid launching synchting using systemd, or configure syncthing-gtk to wait for the syncthing daemon.

Accessing the web-interface

Configuration

After installation Syncthing already has a proper start-up configuration. You may now add new servers and/or folders by visiting the web interface. For detailed instructions on how to set up a simple network, read Syncthing's getting started.

After a successful first start, it will create the default repository at ~/Sync. You can see this in the web admin interface. On the right is the list of nodes you have added. On the left is the list of repositories, which are folders you can choose to share with other nodes.

To add another node, click "Add Node" underneath the list of nodes. You will be prompted for their Node ID (which can be found on the other machine by clicking Edit > Show ID) as well as a short name and the address.
If you specify "dynamic" for the address, the syncthing announce server will be used to automatically exchange addresses between nodes. If you want to know more about Node IDs, including the cryptographic implications, you can read the appropriate Syncthing documentation page.

After saving the configuration, you will be prompted to restart the syncthing server, and once restarted, the changes will be applied.

Next, you can either change the configuration of the default node (click its name and then Edit), or create a new one to share data with. Simply tick the node you wish to share the data with, and they will have permission to access it.

Local network setup

In the typical case several machines, like laptops and androids, share a local area network (LAN) behind a network address translation (NAT) router, it is advised for a versatile configuration to:

Activate both local and global discovery on each node to allow discovery in all situations, including when a mobile device leaves the LAN and connects to the internet from the outside,

Use a different listen address port for each machine, like tcp://:22010, tcp://:22011, tcp://:22012 and so forth. This will differentiate them on the global discovery servers and avoid the "Connected to myself - should not happen" message on the other local devices whenever they leave the NAT.

Enable if possible UPnP port forwarding or manually forward each port. When a node is discovered, Syncthing will first try to use the listening port of the new node. However, if the incoming port is closed on the remote server end, the local listening port will be used instead. If this one appears to be closed as well, Syncthing will attempt to use UPnP to open the port at the NAT router level. If this is not desirable or not possible, each port should be manually forwarded to the right machine on the LAN. Eventually, if no open port can be found on both sides, relaying will be used.

Participate in the infrastructure

Run a relay

Syncthing has the ability to connect two devices via a relay when it is not possible to establish a direct connection between them. Relayed connections are end-to-end encrypted in the usual manner, so the relay has no insight into the connection other than the knowledge of the IP addresses and device IDs.

Note: The relay listens by default to port 22067 for data and 22070 for service status (used for public statistics), they should therefore be open for TCP connections. The default ports can be respectively overridden with the -listen and -status-srv options if necessary.

Run a discovery server

Global discovery is used by Syncthing to find peers on the internet.
Any device announces itself at startup to the discovery server which stores the device ID, IP address, port and current time.
Then on request, for a given device ID, it returns the information stored in JSON format, for instance.

The discovery server requires certificates to run, which should ideally be placed in /var/discosrv. The user/group syncthing needs permissions to be able to read the certificate files. You need to edit the systemd unit file to correctly point to the certificates (and to undertake any other configuration change you may want, see list).

To point the client to your discovery server, change the Global Discovery Servers variable under Settings to https://yourserver:8443/ (default port) or whatever port you have reconfigured to. The variable takes a comma-separated list of discovery servers. It is possible to include multiple ones, including the default one.

If you are using self-signed certificates, the client refuses to connect unless you append the discovery server ID to its domain. The ID is printed to stdout upon launching the discovery server. Amend the Global Discovery Servers entry to add the ID: https://yourserver.com:8443/?id=AAAAAAA-BBBBBBB-CCCCCCC-DDDDDDD-EEEEEEE-FFFFFFF-GGGGGGG-HHHHHHH.

Tips and tricks

Use inotify

This article or section is out of date.

Reason: inotify is deprecated and is now implemented within syncthing (Discuss in Talk:Syncthing#)

Inotify (inode notify) is a Linux kernel subsystem that acts to extend filesystems to notice changes to the filesystem, and report those changes to applications. Syncthing does not support inotify yet but there is an official extension module which talks to the Syncthing REST API. The usage of inotify avoids expensive rescans every minute. The inotify extension can be installed with the syncthing-inotify package. Restartsyncthing.service for change to take effect.

Note: There is no need to enable the syncthing-inotify service when using the syncthing service.

Alternatively, inotify support is provided by syncthing-gtk (which does not depend on syncthing-inotify) but in this case inotify will only work while the GUI is running.

Tip: To prevent errors like Too many open files, increase the default fs.inotify.max_user_watches value, by appending the following line:

/etc/sysctl.d/40-max-user-watches.conf

fs.inotify.max_user_watches=524288

Stop journal spam

Syncthing can be quite noisy even while it is not doing anything. The service ExecStart can be overridden to filter output directly without an extra script (adjust "grep" as needed):

Run in VirtualBox

It is possible to have Syncthing connect both locally and globally within a VirtualBox virtual machine (VM) while keeping its network adapter in the standard NAT mode (as opposed to bridged networking attached to the host computer's adapter).

To enable this mode, Syncthing should listen to a port in the VM different from the listening port already used by the host.
For example, if the default 22000 port is used by the host, one could use 22001 in the VM.
The listening port in the VM can be changed through Syncthing's Sync Protocol Listen Addresses to tcp://:22001 in the GUI Settings.

The 22001/TCP port of the host will need to be forwarded to the guest in this configuration. This can be done with the following command:

$ VBoxManage modifyvm myvmname --natpf1 "syncthing,tcp,,22001,,22001"

In this setup, relaying should not be necessary: local devices can connect to the VM on port 22001 while global devices are accessible as long as they have themselves an open port.

Note: local discovery in this setup is limited because the discovery listening port 21027 is already used by the host. The guest is therefore not able to build a table of local announcements though it can still broadcast to the local network via the VM NAT and announce itself. The steps described above allow to run a functioning server in the default NAT configuration but bridged networking is recommended for an optimal setup.

Running through a proxy

Sometimes it is necessary to run Syncthing as service through a proxy. According to https://docs.syncthing.net/users/proxying.html it is necessary to specify all_proxy environment variable, and it must indicate a socks5 proxy type.

If the service is ran from an script or command line, you can add this before call to Syncthing: